If the screen view is not in a place where charts are located then it will not show any chart keys. Try zooming out until piano keys show up.

Check your Options→Display→Advanced→“Chart Zoom/Scale weighting” For most vector chart the level would be “0”. If for example “5” the chart bar will be crowded and poor performance.

1. Only the charts belonging to the chart “family” viewed at the moment are highlighted.
2. You've three families; CM93 yellow, ENC green and rasters blue.
3. I you show CM93 charts neither of the other two will highlight.
4. If you show a raster chart only other rasters will highlight on mouse over.
5. The same goes for highlight of ENC cells.
6. Consequently will a ENC not quilt with a raster chart at the same time, or vice versa.
7. But as a kind of inconsistency will a raster quilt with CM93 if no rasters are available beside another raster chart. Very handy!
8. To swap chart family to be shown you have to click a chart bar belonging to desired chart family.

If you are actually asking why you don't see the chart cell adjacent to the one being displayed as well, it is because you have disabled quilting and are in single chart mode, to switch back, press “q” or use the hamburger icon in the lower right corner to invoke the chart canvas options menu and turn quilting back on.